U.S. Pat. No. 4,622,551 discloses a communications bus, including an industrial communications unit (ICU) and a master and one or more remote stations. An ICU is located in the master station and in each remote station. Each ICU reads and writes data subject to clock pulses in data frames. The ICU located in the master station transmits data to the ICUs in the remote stations and receives data communicated by the remote stations. The ICUs located in the remote stations transmit and receive data to and from the master. The data communicated between the master and remote stations includes various types of inputs and output into and out of the master and remote stations. For example, when a passenger activates a hall call button, a bit within a data frame is input to a remote station associated with that hall call button and that remote station outputs a bit to the master station. In response, the elevator system sends an elevator to the passenger, and an activation signal from the master station to a remote station associated with a bell activates that bell at the floor landing to announce the arrival of the elevator. Presently, if the elevator arrives but no bell is heard, there is no way to determine whether or not the activation signal was sent or the bell is broken, and the elevator system software is therefore defective.
If an elevator mechanic could display the data frames sent or received by a master or remote station, he could do a better job at troubleshooting the elevator system. That is, if at the landing he saw that the activation signal bit was sent to the remote station, he could immediately replace the bell and avoid having to investigate the software in the machine room and the bell. Presently, there is no way to display the data frames communicated on the communication bus.